The present invention relates to the detection of a short circuit condition in a load and, more particularly, it relates to the detection of a short circuit to battery condition in a remote low-side driven load.
Low-side switching systems are widely employed in automotive applications, such as in the control of devices, such as fuel solenoids. A typical low side driver includes protection for a short circuit condition in the load, that is, it includes a short circuit to battery protection circuit.
In many applications, it is desirable to provide a low-side driver at a load positioned in a location remote from the microprocessor controlling it. For example, it may be necessary to provide a driver for a fuel solenoid at a location far from the engine controller unit. In this type of application, it is critical to keep the number of conductors from the microcontroller to the remote driver to an absolute minimum. The reduction by even one conductor results in a great cost savings in a mass produced product. It is therefore desirable to utilize a single conductor to send control signals to a remote driver, and to receive fault signal feedback over the same conductor.
Also, there are situations where an existing driver circuit must be used to drive a load, however, the driver circuit is not adequately rated for the application. For example, the driver circuit may be rated for only one amp while a current of three amps is required. The existing driver may be part of a larger system that is already in production, thus it may not be easily modified due to cost factors. Therefore, it may be necessary to utilize the existing driver to drive a second remote driver rated for three amps. As described above, it is desirable to keep the number of conductors between the drivers to a minimum.
A high-side switching system used for vehicle AC regulators is disclosed in U.S. Pat. No. 5,166,852 to Sano. The Sano system comprises a detection circuit for detecting the removal of an external ground terminal from a load, e.g., an electronic device, and a protection circuit for protecting the circuits of the electronic device in response to a signal from the detection circuit. The protection circuit includes a low voltage protection circuit for blocking the operation of an output transistor of the electronic device, a memory circuit responsive to signals from both the detection circuit and the low voltage protection circuit, and an input cut-off circuit for cutting off input signals to the electronic device.
U.S. Pat. No. 5,138,516 to Chapman describes a driver circuit with a minimum number of interconnections between it and an output driver circuit, that controls the operation of the output driver circuit. The driver circuit additionally senses fault conditions within the output driver device. However, as is clear from FIG. 1 of the Chapman drawings, the circuit requires a minimum of two interconnections between itself and the output driver circuit.